Gas separator and method for preparing it

ABSTRACT

A gas separator is here disclosed in which a metal for separating a gas is filled into pores opened on the surface of a porous substrate to close them. The thus constituted gas separator can prevent a material gas from leaking into a purified gas. A method for preparing the gas separator is also disclosed which comprises an activation step of immersing the porous substrate having a pair of surfaces in a solution containing an activated metal, while a pressure difference is set between the pair of surfaces, and a chemical plating step of filling the metal for separating the gas into the pores opened on the surface of the porous substrate to close these pores by chemical plating.

TECHNICAL FIELD

The present invention relates to a gas separator for separating aspecific gas from a mixed gas by diffusion, and a method for preparingthe same.

BACKGROUND ART

Heretofore, as a technique for obtaining a specific gas from a mixedgas, there is known a separation method by the use of an organic or aninorganic gas separating film. Among the separating films, examples of ahydrogen separating film for use in a film separation method includeorganic polymeric films of polyimide, polysulfone and the like, andinorganic compound films of palladium, palladium alloys and the like,and examples of an oxygen separating film include films of silver andsilver alloys. The palladium film and the palladium alloy films haveheat resistance and can obtain extremely high-purity hydrogen.

Palladium and the palladium alloys have characteristics which allowhydrogen to be dissolved therein and which allow hydrogen to permeatetherethrough, and by the utilization of the characteristics, a thin filmcomprising palladium or the palladium alloy has been widely used as agas separator for separating hydrogen from a mixed gas containinghydrogen. However, the thin film comprising palladium itself is weak inmechanical strength, and so, in Japanese Patent Application Laid-openNo. 273030/1987, palladium or the palladium alloy is deposited on thesurface of an inorganic porous support of a porous glass, porousceramics, a porous aluminum oxide or the like to increase the mechanicalstrength of the thin film comprising palladium or the palladium alloy.

Japanese Patent Application Laid-open No. 146122/1991 discloses a methodfor preparing a hydrogen separator which comprises first forming apalladium thin film on the surface of a heat-resistant porous substrateby a chemical plating process, and further forming a silver thin film onthe palladium thin film by the chemical plating process, followed by aheat treatment. According to this disclosed method, the hydrogenseparator having the porous substrate and the palladium alloy thin filmcovering it can be obtained. In this palladium alloy thin film,palladium and silver are uniformly distributed by the above-mentionedheat treatment.

In addition, U.S. Pat. No. 3,359,705 discloses a silver thin film forseparating oxygen.

However, these gas separators have a drawback that a material gas to besubjected to the gas separation leaks into a purified gas through holes(hereinafter referred to as "throughhole-defects") which extend throughthe gas separating film comprising the metal for separating the gas.Therefore, the concentration of hydrogen in the purified gasdeteriorates as much as the leaked material gas. For example, JapanesePatent Application Laid-open No. 273030/1987 discloses a method forpreparing a hydrogen separating film using palladium or the palladiumalloy in which the surface of an inorganic porous material is chemicallyactivated, and the palladium thin film is then deposited thereon by thechemical plating process. However, the palladium film formed by thechemical plating process has the holes extending through the palladiumfilm, and the material gas inconveniently flows into the purified gasthrough these holes. In the method disclosed in this publication, thepalladium film is formed on the surface of the porous material, but thispalladium film is not formed in the pores.

Furthermore, in Japanese Patent Application Laid-open No. 171617/1988,there is disclosed a method for preparing a hydrogen separating film inwhich palladium is supported on an inorganic porous film, and thismethod comprises vapor-depositing palladium or the palladium alloy onthe inorganic porous film by sputtering or the like, immersing it in anaqueous [Pd(NH₃)₄ ]Cl₂ solution, and then carrying out a vacuumdeaeration treatment via the inorganic porous film to vaporize asolvent, thereby supporting palladium on the inorganic porous film.However, according to an example, this hydrogen separating film allowsnot only hydrogen but also nitrogen to permeate therethrough, andtherefore it is apparent that the pores in the inorganic porous film arenot closed with palladium. Moreover, palladium is held on the porousfilm by depositing it or vaporizing the solvent from the aqueouspalladium solution, but the laid-opened publication has not anydescription regarding a chemical plating method for reducing divalentpalladium ions contained in [Pd(NH₃)₄ ]Cl₂.

The silver thin film disclosed in U.S. Pat. No. 3,359,705 and thehydrogen separator described in Japanese Patent Application Laid-openNo. 146122/1991 have a similar problem that the material gas flows intothe purified gas.

In order to remove these throughhole-defects, there is a method ofthickening the gas separating film comprising the metal for separatingthe gas, but this method has a problem that a gas permeability of thegas separating film deteriorates and hence a gas separation efficiencyalso deteriorates.

Additionally, this method also has a problem that adhesive propertiesbetween the gas separating film and a substrate such as the porous filmare weak, and when the hydrogen separator obtained by the method isactually used in a gas separation process, the gas separating film peelsin a short period of time. In consequence, such a hydrogen separatorcannot be used continuously for a long term in order to do the gasseparation.

DISCLOSURE OF THE INVENTION

Thus, the present invention is made on the background of the problems ofthe above-mentioned conventional techniques, and an object of thepresent invention is to provide a gas separator which can prevent amaterial gas to be subjected to a gas separation from leaking into apurified gas.

The present invention provides a gas separator comprising a poroussubstrate having pores opened on its surface and a metal for separatinga gas, said metal for separating the gas being filled into the pores inthe porous substrate to close them.

In the present invention, the metal for separating the gas preferablycovers at least a portion of the surface of the porous substrate to forma thin film thereon.

Furthermore, in the present invention, a depth of the metal forseparating the gas which penetrates into the porous substrate ispreferably in the range of 1 to 30 μm from the surface of the poroussubstrate.

In the present invention, the metal for separating the gas is preferablypalladium, an alloy mainly comprising palladium or an alloy containingpalladium.

The present invention provides a method for preparing a gas separatorhaving a porous substrate with a pair of surfaces which comprises anactivation step of immersing the porous substrate in a solutioncontaining an activated metal, while a pressure difference is setbetween the pair of surfaces of the porous substrate, whereby thesolution is allowed to penetrate into pores opened on one of the pair ofsurfaces of the porous substrate, and a chemical plating step ofdepositing a metal for separating the gas in the pores in the poroussubstrate by chemical plating, whereby the metal for separating the gasis filled into the pores to close them.

Furthermore, according to the present invention, there is provided amethod for preparing a gas separator which has an activation step and achemical plating step, and in the activation step, one surface of theporous substrate is immersed in a solution containing an activated metalso that the pressure applied on the one surface may be higher than thepressure applied on the other opposite surface of the porous substrate,whereby the solution is allowed to penetrate into pores opened on theone surface of this porous substrate, and in the chemical plating step,a metal for separating a gas is deposited in the pores in the poroussubstrate, whereby the metal for separating the gas is filled into thepores to close them.

In the present invention, the metal for separating the gas is preferablypalladium, an alloy mainly comprising palladium or an alloy containingpalladium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative view showing a section of a gas separator ofthe present invention.

FIG. 2 is an illustrative view for the description of a gas purificationmethod using the gas separator of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A gas separator 1 of the present invention has a porous substrate 2 anda metal 3 for separating a gas. The porous substrate 2 is porous, and soit has many pores 5, and some of the pores extend to the surface of theporous substrate 2 and they are opened thereon. In the presentinvention, the metal 3 for separating the gas is filled into the pores 5opened on a porous substrate surface 2a to close them. In consequence,when a material gas to be subjected to a gas separation by the gasseparator 1 is passed through the pores 5 in the porous substrate 2, aspecific gas permeates the metal 3 for separating the gas, therebyseparating the specific gas from the material gas. Furthermore, in thegas separator 1 of the present invention, the metal 3 for separating thegas is filled into the pores 5 to close them, so that the material gasis prevented from leaking into a purified gas. Therefore, for example,in the case of the gas separator of the present invention in which apalladium alloy is used, a hydrogen gas having a purity of 99% or morecan be obtained, and usually, the hydrogen gas having a purity of 99.9%or more can be obtained.

As the porous substrate 2, a material which does not react with thematerial gas is preferable. Typical examples of the porous substrate 2include alumina, silica, silica-alumina, mullite, cordierite, zirconia,carbon, porous metals and porous glasses.

This porous substrate has many three-dimensionally connected fine pores.The diameter of these pores is preferably in the range of 0.003 to 20μm, more preferably 0.005 to 5 μm, most preferably 0.01 to 1 μm. If thepore diameter is less than 0.003 μm, resistance to the passage of thegas is large. On the other hand, if it is more than 20 μm, when themetal 3 for separating the gas is deposited on and filled into the poresby chemical plating to close them, an excessively long reaction time isrequired inconveniently. Moreover, when a film, i.e., a gas separatingfilm 4 covering the porous substrate 2 is present, pinholes are liableto be formed in the gas separating film 4 inconveniently. Such a poroussubstrate can be obtained, for example, by a process described inJapanese Patent Application Laid-open No. 273030/1987.

The diameter of the pores in the porous substrate is preferablyuniformized, because the uniform diameter permits easily regulating thedepth of a solution which penetrates into the porous substrate in theactivation step or the chemical plating step, and thus permits easilyand uniformly maintaining the depth of the metal for separating the gaswhich penetrates in the porous substrate. No particular restriction isput on the thickness of the porous substrate 2, so long as the poroussubstrate 2 can hold a sufficient mechanical strength in a useenvironment.

Moreover, the porous substrate 2 preferably has a planar shape, and theplanar shape include a plane shape and a curved shape. In addition, itnaturally includes a tubular shape which corresponds to a closed curvedshape. In the case of the tubular shape, the shape of its section isoptional, but the tubular substrate having a circular section is easilyavailable and preferable. Furthermore, the gas separator or the poroussubstrate 2 may have a plate shape. In this case, it can take anoptional shape in compliance with its use purpose. The porous substratepreferably has a pair of surfaces.

The kind of metal 3 for separating the gas depends upon the kind of gasto be purified. For example, in order to purify a hydrogen gas,palladium, an alloy mainly comprising palladium or an alloy containingpalladium is selected. For the sake of the separation of oxygen, a thinfilm of silver or an alloy mainly comprising silver, or a thin film ofan organic material is used.

In the present invention, as shown in FIG. 1, the metal 3 for separatingthis gas is filled into the pores 5 opened on the surface 2a of theporous substrate 2 to close these pores 5. In FIG. 1, the metal 3 coversthe surface 2a of the porous substrate 2 to form the gas separating film4. However, in the gas separator 1 of the present invention, the metal 3for separating the gas present in the porous substrate 2 functions toseparate the gas, and hence such a gas separating film 4 as shown FIG. 1is not essential.

However, it is preferable that the metal 3 for separating the gas coversat least a part of the surface 2a of the porous substrate 2 to form thegas separating film 4 thereon, because the permeation of the gas to bepurified through the metal 3 for separating the gas can be more assured.In this case, the metal 3 may cover a part alone of the porous substratesurface 2a, whereby in the covered part, the permeation of the gas to bepurified through the metal 3 for separating the gas can be more assured.

The gas separating film 4 preferably covers the porous substrate surface2a. The metal 3 for separating the gas, which is filled into the poresopened on the surface of the porous substrate to close these pores, ispreferably continuously connected with the metal for separating the gaswhich constitutes the gas separating film 4, as shown in FIG. 1, wherebyadhesion between the gas separating film 4 and the porous substrate canbe improved and the peeling of the gas separating film 4 from the poroussubstrate surface 2a can be sufficiently prevented.

The thickness of the gas separating film 4 is preferably 50 μm or less,more preferably 20 μm or less. If the thickness of the gas separatingfilm 4 is in excess of 50 μm, a long time is taken for the material gasto diffuse in the gas separating film at the time of gas separation bythe gas separator, so that a treatment time is prolonged inconveniently.

The depth of the metal 3 for separating the gas which penetrates intothe porous substrate 2 is preferably in the range of 1 to 30 μm, morepreferably 1 to 20 μm, most preferably 1 to 10 μm from the surface ofthe porous substrate. If this depth is less than 1 μm, the closure ofthe pores with the metal 3 for separating the gas is not sufficient, andthe material gas may leak into the purified gas. In addition, when thegas separating film 4 is formed, this gas separating film 4 is liable topeel from the porous substrate surface 2a. On the other hand, if thisdepth is more than 30 μm, a long time is taken for the gas to beseparated to diffuse in the metal 3 for separating the gas at the timeof gas separation by the gas separator 1, so that a gas separation timeis prolonged inconveniently.

In the case that the porous substrate 2 has a tubular shape, the surface2a of the porous substrate having the pores into which the metal 3 forseparating the gas is filled may be present on an outer side or an innerside of the tubular porous substrate.

In the case that the metal 3 for separating the gas comprises apalladium alloy, the content of metals other than palladium ispreferably in the range of 10 to 30% by weight, as described in"Hydrogen Permeable Palladium-Silver Alloy Membrane Supported on PorousCeramics", Journal of Membrane Science, Vol. 56, p. 315-325 (1991) andJapanese Patent Application Laid-open No. 295402/1988. The main purposeof using palladium in the form of the alloy is to prevent theembrittlement of palladium with hydrogen and to improve a separationefficiency at a high temperature. It is preferable for the prevention ofthe embrittlement of palladium with hydrogen to contain silver as ametal other than palladium.

Next, a method for preparing the gas separator regarding the presentinvention will be described in detail.

The method for preparing the gas separator of the present invention hasan activation step and a chemical plating step. In this activation step,one surface of the porous substrate is immersed in a solution containingan activated metal so that the pressure applied to the one surface maybe higher than the pressure applied to the other opposite surface of theporous substrate, whereby the solution is allowed to penetrate into thepores opened on the one surface of the porous substrate to which thehigher pressure is applied. Owing to the presence of such a pressuredifference, the activated metal can be deposited not only on the surfaceof the porous substrate but also on the inner surfaces of the poresopened on the surface of the porous substrate. On the surface on whichthe activated metal has been deposited, a metal for separating the gaswill be further deposited by the next chemical plating step.

In this activation step, the one surface of the porous substrate ontowhich the higher pressure is applied is required to be immersed in thesolution, but the other opposite surface does not have to be immersed inthe solution. For example, in the case that the tubular porous substrateis used, its outer surface may be immersed in the solution containingthe activated metal, and the inside portion of the tube can be sucked bya vacuum pump. Alternatively, the outer surface of the tubular poroussubstrate may be immersed in the solution containing the activatedmetal, and the pressure may be applied to this solution to maintain theinside portion of the tube at a constant pressure. In either case, theouter surface and the inner surface of the tube can be inverted, and theinner surface of the tube is immersed in the solution and the pressurecan be changed.

As the activated metal, a compound containing divalent palladium ionscan be suitably used. Concretely, the activation step can be achieved byalternately immersing the porous substrate in an aqueous hydrochloricacid solution of palladium chloride and an aqueous hydrochloric acidsolution of tin chloride, and while the immersion is done in eithersolution, the predetermined pressure difference is preferablymaintained.

In the next chemical plating step, electroless plating is carried out bythe use of at least the metal for separating the gas and a platingsolution containing a reducing agent to deposit the metal for separatingthe gas in the pores of the porous substrate, whereby the metal forseparating the gas is filled into the pores to close them. In thischemical plating step, the one surface of the porous substrate alreadytreated in the above-mentioned activation step is treated. For example,the chemical plating step can be achieved by replacing theabove-mentioned solution used in the activation step with the suitableplating solution.

Also in this chemical plating step, it is preferable that one surface ofthe porous substrate is immersed in the plating solution containing atleast the metal for separating the gas and the reducing agent so thatthe pressure applied to the one surface may be higher than the pressureapplied to the other opposite surface of the porous substrate, in thesame manner as in the above-mentioned activation step. This pressuredifference makes it easy for the plating solution to permeate into thepores opened on the surface of the porous substrate. As described above,the portion on which the activated metal has been deposited in theactivation step is plated in this chemical plating step.

The depth of the penetrated metal for separating the gas from thesurface of the porous substrate can be adjusted by controlling animmersion time in the chemical plating step, a temperature of theplating solution, a difference between the pressures applied to both thesurfaces of the porous substrate, and the like.

For the sake of the hydrogen separation, a known chemical platingsolution containing palladium is used, and for the oxygen separation, aknown chemical plating solution containing, for example, silver nitrate,EDTA, aqueous ammonia and hydrazine is used.

In the case that the gas separator for separating hydrogen is prepared,it is preferable that after the chemical plating of palladium, silver isfurther chemically plated on the palladium-deposited surface, followedby a heat treatment, to mutually diffuse palladium and silver and tothereby form an alloy of palladium and silver.

EXAMPLES

Now, the present invention will be described in detail with reference toexamples.

Examples 1-3

In the first place, a porous substrate was subjected to an activationtreatment. A porous α-alumina cylindrical tube having an outer diameterof 10 mm, an inner diameter of 7 mm, a length of 300 mm and a fine porediameter of 0.1 μm was used. The outer surface of this alumina tube wasimmersed for 1 minute in a 0.1% aqueous hydrochloric acid solutioncontaining 0.1% by weight of SnCl₂.2H₂ O, and on the other hand, theinside portion of the tube was sucked by a vacuum pump to reduce thepressure of the inside portion. Next, the outer surface of this tube wasimmersed for 1 minute in a 0.1% aqueous hydrochloric acid solutioncontaining 0.01% by weight of PdCl₂. At the time of the immersion, theinside portion of the tube was sucked by the vacuum pump to reduce thepressure of the inside portion. This immersion treatment was repeated 10times in each of both the aqueous hydrochloric acid solutions.

Next, palladium was chemically plated. [Pd(NH₃)₄ ]Cl₂.H₂ O (5.4 g),2Na.EDTA (67.2 g), aqueous ammonia having an ammonia concentration of28% (651.3 ml) and H₂ NNH₂.H₂ O (0.46 ml) were added to 1 l of deionizedwater to prepare an aqueous solution, and the outer surface of theporous alumina tube which had been subjected to the above-mentionedactivation treatment was immersed in this aqueous solution whosetemperature was controlled to 50° C. This immersion time was changed toadjust a thickness of a thin film covered on the surface of the poroussubstrate and a depth of the solution which penetrated into the poroussubstrate.

Next, silver was chemically plated. AgNO₃ (3.46 g), 2Na.EDTA (33.6 g),aqueous ammonia having an ammonia concentration of 28% (651.3 ml) and H₂NNH₂.H₂ O (0.46 ml) were added to 1 l of deionized water to prepare anaqueous solution, and the outer surface of the porous alumina tube whichhad been subjected to the above-mentioned activation treatment wasimmersed in this aqueous solution whose temperature was controlled to50° C. This immersion time was changed as shown in Table 1, and silverwas then chemically plated so that a weight ratio of palladium:silvermight be 80:20.

In the last place, the thus treated porous alumina tube was maintainedat 900° C. for 12 hours to carry out a heat treatment, whereby palladiumand silver were mutually diffused, and an alloy of palladium and silverwas formed to obtain a gas separator.

For the thus obtained gas separator, an airtight test was carried out.An argon gas was introduced into an outer peripheral portion of thealumina tube, and a pressure of 9 kg weight/cm² was maintained. At thistime, an amount of the gas leaked into the alumina tube was measured.

Furthermore, for the gas separator, a hydrogen separation test wascarried out. A mixed gas comprising 80% by volume of hydrogen and 20% byvolume of carbon dioxide was used as a material gas. A schematic view ofa test device is shown in FIG. 2. First, a chamber 7 was heated up to500° C. Next, the above-mentioned mixed gas 17 having a pressure of 9 kgweight/cm² was introduced into the outer peripheral portion of analumina tube 6 at 2 N liter (i.e., a volume at room temperature was 2liters) per minute. Argon having a pressure of 1 kg weight/cm² wasintroduced as a sweep gas 18 into the alumina tube at 0.1 N liter perminute. A purified gas 19 thus obtained was quantitatively analyzed by agas chromatography to inspect a gas permeation rate of the purified gasand a hydrogen concentration in the purified gas.

Incidentally, in FIG. 2, a mixed gas 17 to be separated was introducedinto the outer peripheral portion of a gas separator 16 through an inletpipe 10. The sweep gas 18 which was a separated hydrogen gas wasintroduced into the gas separator 16 through an inlet pipe 8. O-rings 15surround the outer peripheries of the gas separator 16 at its both endportions to prevent the leakage of the gas.

For example, in Example 1, a gas permeation rate per minute in 1 cm² ofthe palladium film of the gas separator was 18 ml, and a hydrogen purityof a purified gas 19 was 99.99% or more.

Furthermore, for the gas separator, a thermal cycle test was carriedout. The gas separator in a hydrogen atmosphere was heated from roomtemperature to 500° C., and then cooled to the room temperature. Thecycle of the heating·cooling was repeated 20 times.

The results of the airtight test, the separation test and the thermalcycle test are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                  Gas Separator                                                                 Film                Airtight Test                                      Thickness Depth Leaked Gas                                                    (μm) (μm) (ml/cm.sup.2 · min)                               ______________________________________                                          Example 1 15 5 0.01 or less                                                   Example 2 5 5 0.01 or less                                                    Example 3 1 4 0.01 or less                                                    Comp. Ex. 1 20 0.5 2                                                          Comp. Ex. 2 10 0.5 5                                                          Comp. Ex. 3 5 0.5 11                                                        ______________________________________                                               Gas Separation Test                                                                          Hydrogen  Thermal                                          Purified Gas Purity Cycle Test                                                (ml/cm.sup.2 · min) (%) (20 times)                                ______________________________________                                          Example 1 18 99.9 or more Not changed                                         Example 2 35 99.0 or more Not changed                                         Example 3 65 99.0 or more Not changed                                         Comp. Ex. 1 20 90 Peeled                                                         (at 9th cycle)                                                             Comp. Ex. 2 39 87 Peeled                                                         (at 13th cycle)                                                            Comp. Ex. 3 70 84 Not changed                                               ______________________________________                                    

Comparative Examples 1-3

In each comparative example, a treatment was carried out under the sameconditions as in the above examples except that the pressure in theinside portion of an alumina tube was not reduced in a porous substrateactivation step. The results are shown in Table 1.

Comparing the examples to the comparative examples, it is apparent thatpalladium can be deposited even within the porous substrate by reducingthe pressure in the alumina tube. Additionally, it is also apparent thatsince a palladium alloy can be filled even into pores in the poroussubstrate to close these pores, the airtight of the gas separator can beimproved, and a hydrogen purity in the purified gas can be remarkablyimproved.

The thermal cycle test is also a parameter indicating adhesiveproperties of the gas separating film to the porous substrate in the gasseparator. Comparing the examples to the comparative examples, it isapparent that in the examples, the peeling of the gas separating filmfrom the porous substrate is more difficult, which indicates that theadhesive properties of the gas separating film to the porous substrateare improved, because in the examples, the metal for separating the gasis filled into the pores opened on the surface of the porous substrateto close them.

In the gas separator of the present invention, the metal for separatingthe gas is filled into the pores opened on the surface of the poroussubstrate to close them, whereby the material gas to be subjected to thegas separation by the gas separator can be prevented from leaking intothe purified gas. Therefore, for example, according to the gas separatorof the present invention using a palladium alloy, a hydrogen gas havinga purity of 99.9% or more can be obtained.

Possibility of Industrial Utilization

Furthermore, when a gas separator of the present invention has a gasseparating film comprising a metal for separating a gas on the surfaceof a porous substrate, the metal for separating the gas is filled intothe pores opened on the surface of the porous substrate to close them,and thus the adhesive properties of the gas separating film to theporous substrate can be improved. This effect is more remarkable, ascompared with the gas separator covering the surface of the poroussubstrate without filling the gas separating film into the pores openedon the surface of the porous substrate.

With regard to a method for preparing the gas separator of the presentinvention, in its activation step, the porous substrate having a pair ofsurfaces is immersed in a solution containing an activated metal, whilea pressure difference is set between the pair of surfaces, whereby thesolution is allowed to penetrate into the pores opened on its onesurface. Next, in a chemical plating step, a metal for separating thegas is deposited in the pores in the porous substrate, whereby the metalfor separating the gas is filled into the pores to close them.

By the use of the gas separator of the present invention, a specific gassuch as hydrogen can be obtained in a high purity from a mixed gas.

We claim:
 1. A method for preparing a gas separator having a poroussubstrate with a pair of opposing surfaces which comprises:an activationstep of immersing the porous substrate in a solution containing anactivated metal, while a pressure difference is set between the pair ofopposing surfaces of the porous substrate, whereby the solution isallowed to penetrate into pores that open onto one of the pair ofopposing surfaces of the porous substrate, and a chemical plating stepof depositing a metal for separating the gas in the pores in the poroussubstrate by chemical plating, whereby the metal for separating the gasis deposited or impregnated into the pores and closes them.
 2. Themethod for preparing a gas separator according to claim 1 wherein themetal for separating the gas is palladium, an alloy mainly comprisingpalladium or an alloy containing palladium.